1. Field of the Invention
This process relates to catalytic reactors having concurrent multiphase reactant feeds. In particular, it relates to a method and apparatus for separating liquid and gaseous phases and distributing the reactants down-flow uniformly onto a bed of catalyst particles.
2. Background of the Invention
In the treatment of hydrocarbons or other organic materials in a petroleum refinery or petrochemical complex, various catalytic processes are employed; for instance, hydrocracking with zeolite catalyst, hydrodesulfurization with Co, Ni and/or Mo catalysts, etc. Often, these processes are carried out in a fixed bed reactor, with multi-phase reactant feedstock mixtures being introduced at an upper reactor inlet for downward co-current flow over the catalyst bed.
In prior reactors, distribution of liquid has been achieved with a horizontal tray or the like mounted within the reactor shell, with perforations, weirs, or multiple conduits for uniformly spreading the liquid over the catalyst bed.
A typical reactor shell has a cylindrical configuration with vertical axial flow; although other reactors may also be employed, such as elongated polygonal or spheroidal shells. Pressure vessels in catalytic hydrogenation processes usually must withstand high pressures, and thus, are constructed to withstand internal pressures of several atmospheres up to hundreds, depending upon the desired pressure of reactant gas. A typical hydrogenation reactor may be constructed of welded 304 stainless, carbon steel or the like.
Retrofitting of catalytic reactors is desirable when a chemical manufacturing complex is altered to accommodate different processes. Many general-purpose pressurized reactors are constructed of welded steel with a length:diameter ratio (L:D) of about 2:1 to 10:1, preferably 4:1 to 6:1. These reactors may be enclosed at top and bottom with bolted or welded hemispheroidal end sections. Fluid inlet and outlet ports, maintenance access holes, and other openings for piping, instrumentation, etc. are provided.
Input gas and liquid reactants may be introduced at the top of the reactor in a mixed stream through a simple inlet conduit, and flow downwardly through the porous reactor bed. In order to maintain homogenous flow throughout the horizontal cross-sectional reactor area, the reactants are distributed over the surface of the catalyst bed. In some prior art reactors, such as disclosed in U.S. Pat. No. 4,126,539 (Derr et al) or in U.S. Pat. No. 3,218,249 (Ballard et al), a distributor tray is mounted over the catalyst bed for receiving vapor and liquid reactants for distribution. While internal arrangements of this type may be satisfactory for original equipment installations, they are difficult to install in pre-existing reactor shells. This difficulty is due to weakening of the reactor shell during welding or other installation techniques. Although it is technically possible to field weld internal distributor components and anneal the structure to retain integrity of the pressure vessel, such modifications are expensive and time-consuming.
Reactor modifications for petrochemical plants may require altering a single-phase system for multi-phase processes or other internal structural changes and/or repiping. Such modifications to existing equipment may expedite process changeover or decrease cost on a new process installation. Known flow nozzle designs are adequate for single phase liquid or gas distribution or when high pressure drop is permissible. However, it has been found that low pressure drop distributors for mixed gas and liquid feed in cocurrent reactors are extremely difficult to install.
Sometimes when smaller reactors are used, there are additional complications. Smaller liquid flows present a more challenging problem of flow distribution within a reactor than do large liquid flows. This is because with conventional pipe distributors, with holes drilled in them, the holes must be of such small size to ensure adequate flow distribution that the holes plug easily. The foraminous distributor of U.S. Pat. No. 4,579,647 which is incorporated by reference, is a good distributor design for retrofitting in existing vessels, but not so good for use in reactors where plugging of holes in the distributor is a problem.
There is still a need for a vapor/liquid distributor which can be retrofitted into existing reactors, and which will be suitable for use even in small reactors, or in any reactors with relatively low liquid flows, or when the liquid stream is likely to coke or have particulate matter in it which would cause plugging of conventional pipe distributors.
A way has now been discovered to achieve satisfactory liquid distribution in such two phase reactors.